1. Field of the Invention
The invention is related to a method for setting laser power, and, more particularly, to a method for setting a laser output power level in an optical disc drive.
2. Background of the Related Art
Optical discs have been developed recently which allow data to be recorded on a data surface of the disc, and a label with a desired design to be printed on a non-data, or label, surface opposite the data surface of the disk. The surface of the disc on which a label is printed is referred to as the label surface of the disc. Labels may be transferred onto the label surface of the disc using a laser etching technology commonly referred to as LightScribe, in which a laser burns or etches an image onto a specially prepared, non-data side of an optical disc.
Generally, laser power required to record data on an optical disc varies based on recording speed and other recording medium characteristics. Typically, an input voltage (DAC) of a Radio Frequency (R/F) Integrated Circuit (IC) is controlled to set laser power at a desired magnitude. However, the actual magnitude of laser power output for a given input voltage (DAC) may differ based on differences or deviations in optical pickups and R/F IC characteristics. Therefore, during manufacture of an optical disc drive, the relationship between an input voltage (DAC) and an actual output laser power (P) associated with the input voltage (DAC) is measured and stored in a ROM (Read Only Memory) for each device, such that an output laser power of a desired magnitude can be set based on the measured result.
Generally, in order to calculate the relationship between the input voltage and the output laser power, actual output laser power is measured using a device specifically designed for that purpose such as, for example, a laser power meter, during manufacture of the optical disc drive. The relationship between the input voltage applied to the R/F IC and the laser power generated from the optical pickup unit is typically at least partially linear. Therefore, a linear equation relating the input voltage (DAC) to the laser power (P), which reflects power setup data for selected points during the manufacturing process, has been widely used to establish this relationship.
When printing a label on a label surface of an optical disc such as, for example, the LightScribe disc discussed above, an input voltage corresponding to a desired laser power is calculated using a linear relationship between the input voltage and the desired laser power detected during the manufacturing process of the optical disc drive. The calculated input voltage is applied to the R/F IC, such that a label-printing operation can be performed with a laser power of predetermined magnitude.
However, this type of label-printing operation requires the laser to output power at a much higher level than would typically be required to perform a recording operation on the data surface of the disc. If the laser output value is increased above a predetermined value based on an increment of the input voltage, the relationship between the input voltage and the laser power is no longer linear, as shown in FIG. 1, and the ratio (i.e., slope) of output laser power to input voltage is gradually reduced. In this manner, if the linear relationship between the input voltage and the output laser power is changed, an unexpected error occurs in a laser power setup process as denoted by ΔPerror=Pactual−Pideal, resulting in a deterioration in printing quality on the label surface of the disc.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.